Method and apparatus for recording data without recording on defective areas of a data recording medium

ABSTRACT

A method of transferring data between a data supply and a disk having a track divided into sectors, each sector having an address recording area followed by a data recording area. The method includes detecting a defective area on a data recording area; writing an address of the defective area on the corresponding address recording area; recording data on the data recording area by detecting the defective area with the address and writing part of the data on the data recording area up to the defective area, and writing the remaining data on the data recording area succeeding the defective area; and retrieving the written data by reading the address of the defective area and then reading the recorded data. The apparatus includes a circuit to record a test pattern on the disk, a circuit to sense the recorded test pattern and provide an address of a defective area, a circuit to write the address on the address recording area, a circuit to write data on the disk, and a circuit to read the recorded area.

BACKGROUND OF THE INVENTION

This invention relates to data storage and retrieval systems and, moreparticularly, to a method and apparatus for detecting defective areas ona recording medium and transferring data between the recording mediumand a data supply unit, bypassing the defective areas.

Various types of information retrieval systems have been developedincluding those which utilize bulk storage devices for processingdigital data. One type of bulk storage device includes a disk filehaving at least one magnetic recording disk in which information isstored on the surfaces of the disk. Each surface has a plurality ofconcentric tracks on which are stored the data, with each track beingdivided into one or more sectors. Typically, the data is recorded oneach track by magnetizing the recording surface. Usually, bits ofinformation are recorded, each of which may be a logic "1" or "0"distinguishable by a change or transition of magnetization of thesurface.

In the manufacture of disks, a magnetic coating is formed on the surfaceof the disk for subsequent magnetization by the disk user in accordancewith the information to be stored. However, various problems occur withinformation storage systems using these magnetic disks due to defectiveareas on the recording surface. There are areas in which there may be nomagnetic coating or an insufficient amount of such coating, i.e.,imperfections, to properly record data on the disk, or to properlydistinguish magnetic transitions when reading the data. One probleminvolves data integrity in that the user may not be assured that thedata is being properly written on or read from the recording surface dueto the defective areas. Another problem is that if the user is readingincorrect data from the recording surface due to the defective areas,then additional time might be used to reread the data until the desiredinformation is retrieved, thereby undesirably increasing throughput.

As a result of these problems, both the manufacturer of the disks, andthe manufacturer of disk drives which write and retrieve the data on thedisks, have taken precautions to minimize the effects of defective areason recording surfaces. After the magnetic coating is placed on therecording surface, the disk manufacturer will test the disk beforedistributing it for use with the disk drives. If too many defectiveareas are found, the disk will be discarded; otherwise, it will bedistributed to the user with a specified number of defective areas onit. This specification may not be entirely satisfactory since during useof the disk additional defective areas may appear if the disk wears ordirt gets imbedded on the disk, or the original defective areas may growin size.

The disk drive manufacturer, on the other hand, may include in the driveor control unit a circuit to detect the defective areas to record thedata on other areas of the recording surface. Consequently, the diskmanufacturer will provide spare areas on which to record data whichcannot be written on the defective areas. In one solution, the disk willhave spare data tracks, while in another approach the disk will have oneor more spare sectors for a given track. Upon detection of a sector of agiven track having a defective area, the disk drive circuit will cause arelocation of all the data intended for that sector onto the spare trackor the spare sector of the given track, depending on the system beingused. In retrieving the recorded data, when the sector having thedefective area is detected, the data will then be read either from thespare track or from the spare sector, depending on the system beingused.

Either of the above disk drive techniques for avoiding recording on thedefective areas results in a loss in data storage capacity. The morespare tracks or sectors needed to account for all the defective areasexisting or anticipated on the recording surface, the less capacitythere is on the disk for storing the data. Also, the time for accessingthe data on recording surfaces having spare recording areas may besignificantly and undesirably increased. For example, in a disk havingthe spare tracks, these may be the inner concentric tracks of therecording surface. If data is being read or written on an outer track onthe recording surface, and a sector of this outer track having adefective area is detected, then additional time will be required tomove the recording head to an inner spare track to read or write thedesired data. Additional time may also then be needed to return therecording head to the outer track to continue reading or writing data onthis outer track. In a system using a spare sector of a given track,when a sector having a defective area is detected, the data transferoperation may have to cease temporarily until the disk can be rotated toposition the spare sector under the recording head; thereafter, the datatransfer operation again may have to cease until the disk again rotatesto position an appropriate nondefective sector of the track under therecording head for reading or writing the data.

Another disadvantage with the above disk drive techniques relates tosmall, newly grown defective areas which cannot be detected due to thesensitivity of the disk drive detector circuit. This will result in aloss in data integrity which may require the disk drive user to rereador rewrite data on the recording surface, thereby undesirably increasingthroughput. Alternatively, the user of the disk drive would have to takeinto consideration these undetectable defective areas on a recordingsurface when planning to use the storage system since such areas mayreduce the specified capacity of the disk. In other words, in utilizingsuch disk drive, the user knows that the disk drive may not be optimumin the sense that additional and undetectable areas will have to beaccounted for in planning the amount of data that can be stored on thedisk.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel apparatusand method which results in the transfer of data between a storagemedium and a data supply unit without recording on the defective areasof the medium.

It is another object of the present invention to provide apparatus andmethods for maximizing storage capacity of a storage medium despite theexistence of defective areas on the medium, while making no compromisein the quality of the usable recording area.

A still further object of the present invention is to provide apparatusand methods which maximize throughput.

A yet further object of the present invention is to minimize oreliminate any preplanning by a disk drive user to account for a growthof defective areas on the recording medium.

These and other objects of teh present invention are obtained through aunique technique for identifying defective areas on a data recordingsurface and for transferring data between the recording medium and adata supply unit. Apparatus and methods are provided for identifyingdefective areas on a recording medium having a track divided into one ormore sectors with each sector having an address recording area and adata recording area. A defective area within a data recording area of asector is detected and an address of the defective area written on thecorresponding address recording area. Apparatus and methods are alsoprovided to write all the data intended for the sector having thedefective area on the data recording area of such sector except on thedefective area. Apparatus and methods are also provided for thenretrieving all the data recorded on the sector having the defectivearea.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a circuit for recording a test pattern on adisk.

FIG. 2 is a block diagram of a circuit for locating defective areas onthe disk.

FIG. 3 is a block diagram of a circuit for writing addresses of thedefective areas on the disk.

FIG. 4A illustrates a waveform for recording the test pattern on thedisk.

FIG. 4B is an illustration of the test pattern waveform which is readfrom the disk.

FIG. 5 is a block diagram of a circuit for writing data on the disk,except over the defective areas.

FIG. 6 is a block diagram of a circuit for reading the data recorded onthe disk with the circuit of FIG. 5.

FIGS. 7A-7C are timing diagrams useful in explaining the operation ofthe circuit of FIG. 5.

FIGS. 8A-8C are timing diagrams useful in explaining the operation ofthe circuit of FIG. 6.

DETAILED DESCRIPTION OF THE DRAWINGS

The circuits shown in FIGS. 1-3 and 5-6 may be divisible into twoseparate systems for carrying out the principles of the presentinvention. The circuits of FIGS. 1-3 may be utilized by a diskmanufacturer to test for defective areas on the disk, and to record anidentification of the detected defective areas on the disk. The circuitsof FIGS. 5-6 may be part of a disk drive made by the disk drivemanufacturer to enable a user of the disk drive and the disks having thedefective areas to transfer data between the disk and a data supplyunit. However, it will be appreciated from the following discussion bythose skilled in the art that all of the these circuits can be embodiedin a single disk drive to store data on the disk except on the defectiveareas and to retrieve such data from the disk. Furthermore, while theinvention will be described in relation to disk storage mediums and diskdrives, it will also be appreciated that the invention can be applied toother bulk storage systems using, for example, magnetic tape.

In FIG. 1 there is shown a disk 10 having a recording surface 12 whichis magnetizable in accordance with well known principles to store bitsof information on discrete areas of the surface. The surface 12 isorganized into a plurality of concentric tracks T and a plurality ofwedge-shaped sectors S. For example, the surface 12 may have eighthundred tracks T₁ -T_(800'), each divided into sixteen sectors S₁ -S₁₆.Each sector S has a sector identification area 14 and a data recordingarea 16.

In addition to other well known information which need not be describedfor purposes of an understanding of the present invention, the sectoridentification area 14 eventually will store an address of a defectivearea within the data recording area 16, and the area 16 eventually willstore the desired data. Thus, the sector identification area 14 willhave an address recording or storage area 14'.

Also shown in FIG. 1 is a circuit 18 for writing a test pattern of bitson any one or more tracks T₁ -T₈₀₀ of the recording surface 12. Circuit18 includes an oscillator 20 which outputs a constant frequency signalover a line 22 to a write trigger 24 which responds to the signal fromoscillator 20 to trigger a write driver 26 via a signal on a line 28.The driver 26 may be a current source which outputs a test patterncurrent signal of constant frequency, shown in FIG. 4A, which is fed toa standard read/write recording head 30 for recording bits on the datarecording areas 16 of each sector S. Oscillator 20 is energized inresponse to a control signal on a line 32 from a sector detector 34 thatresponds to the output from a head 36 which, for example, sense aconventional prerecorded sector mark (not shown) at the beginning ofeach sector identification area 14 of each sector S. Head 36 anddetector 34 also detect an end of sector mark (not shown) at the end ofeach sector S to produce a control signal on line 32 to de-energizeoscillator 20. A motor 38 rotates the disk 10 to move the sectors S pastthe heads 30 and 36.

In the operation of the circuit 18, the head 30 will be positioned overa particular track T and motor 38 energized to rotate the disk 10. Whena sector S is detected by the head 36 and detector 34, oscillator 20will be energized by the control signal on line 32 so that the head 30will record the test pattern signal shown in FIG. 4A on thecorresponding data recording area 16. When the end of sector mark isdetected, oscillator 20 will be de-energized to avoid writing the testpattern signal on the area 14 of the succeeding sector S. This signalwill be recorded on each sector S of the track T and, thereafter, thehead 30 may be moved by a servo mechanism (not shown) to a new track Tto record the test pattern in the smae manner on each of its sectors S.

As one example, each data recording area 16 of each sector S of eachtrack T may have a capacity of 4096 bits or 512 bytes, there being 8bits per byte. Accordingly, the test pattern signal shown in FIG. 4Aillustrates 4096 half cycles numbered 1-4096, with each half cyclecorresponding to 1 bit.

With the test pattern signal recorded on all tracks T₁ -T₈₀₀ of thesurface 12, a circuit 40 shown in FIG. 2 then will be utilized to detectand identify defective areas on the surface 12. In this FIG. 2, likereference numerals are used to indicate like elements shown in FIG. 1.Circuit 40 includes a read amplifier 42 which amplifies the test patterninformation on surface 12 read by the head 30 and provides an outputsignal over a line 44 to a detector 46 and a counter 48, this outputbeing shown in FIG. 4B. As indicated in FIG. 4B, each half cycle of thiswaveform corresponds to a bit recorded on data recording area 16 withthe waveform of FIG. 4A.

Detector 46 is an amplitude detector which senses the output signalshown in FIG. 4B from the read amplifier 42 and produces an outputsignal on a line 50 when there is a reduction in amplitude greater thana predetermined value, as will be more fully described. Counter 48,which may be either a bit or byte counter, but prefereably in thelatter, is activated by sector detector 34 at the beginning of each datarecording area 16 of each sector S to count the test pattern data fromamplifier 42 after the start of sector mark is detected. Counter 48 willbe reset at the end of each recording area 16 in a well known manner,such as by detecting the end of sector mark (not shown) to begincounting test pattern data on the next data recording area 16. An Andgate 52 receives the count in counter 48 as one input over a line 54 andthe output of detector 46 on line 50 as another input which enables thegate 52 to transfer this count to a memory 56 for storage.

In the operation of circuit 40, the head 30 will be positioned over asingle track T and the motor 38 energized. As head 30 reads the testpattern data recorded on surface 12 with the circuit 18, amplifier 42will output the signal shown in FIG. 4B to detector 46. At this timehead 36 and detector 34 will have detected the start of sector mark in asector so that counter 48 will begin counting the data from amplifier42. If an area on surface 12 for the recording of a bit is defective,there will be an amplitude variation in the output signal, for example,as shown in FIG. 4B for bit 221. Consequently, upon detection of thisamplitude variation, gate 52 will be enabled to transfer the count incounter 48 into memory 56 to store a count or address corresponding tothis defective area. If counter 48 were a byte counter, this countstored in memory 56 would be 27. As each sector S of a given track Trotates beneath heads 30 and 36, defective areas will be detected andaddresses to these defective areas stored in memory 56 as justdescribed. After testing a given track T for the defective areas andidentifying them in memory 56 with an address, the head 30 will be movedto a new track T to detect and identify in the same manner the defectiveareas on this new track.

Before continuing with a discussion of the circuit shown in FIG. 3, itwill be helpful to discuss more specifically one feature of detector 46for this invention. As illustrated in FIG. 4B, there is a reduction inthe amplitude of the read-back signal corresponding to bit 221. Thisamplitude reduction indicates that the recording area on surface 12 forbit 221 of a given sector S and track T does not have a satisfactorymagnetizable coating as in the other bit areas. While it may be suitablefor purposes of data integrity to use initially a recording surface 12in which there is a reduction in amplitude by as much as fifty percent,this would not be satisfactory in the long term since continued use maycause the surface 12 to be worn such that there might be a reduction inamplitude greater than fifty percent. Consequently, detector 46 could bea very sensitive amplitude detector which can detect a reduction inamplitude of only about ten percent. Thus, if there is a relativelysmall reduction in amplitude of the signal corresponding to bit 221,this will be detected by detector 46 to enable gate 52.

Moreover, when the signal of FIG. 4B indicates that there is even aslittle as a ten percent reduction in amplitude for a particular bit, theprobability is relatively high that during use of the recording surface12 this potentially defective area will grow by several bits so that,for example, eventually the entire defective area may be ten bits wideextending from bits 217 to 226. Therefore, provision is made in thecircuits of FIGS. 5-6 to account for this potential growth up to amaximum bit length, which throughout this disclosure will be assumed tobe 2 bytes or 16 bits.

It also should be noted that for purposes of simplifying the descriptionof the invention, it is being assumed that the recording surface 12 hasbeen manufactured with only one defective bit area or potentiallydefective bit area per sector S of each track T, such as the area forbit 221 in the example given above. If there is detected during testing,more than one such defective bit area per sector S per track T, then thedisk 10 may be considered to be unsuitable for use and, therefore, maybe discarded. However, it will be appreciated that the principles of thepresent invention will still apply if in fact there is more than onesuch defective bit area spaced outside the maximum bit length accountedfor in detecting bit 221. For example, if a disk 10 having these twodefective bit areas is considered to be acceptable, then two addressesper sector S per track T could be stored in memory 56.

With the testing completed and the addresses stored in the memory 56, itis now necessary to record these addresses on the appropriate addressrecording areas 14' of each sector S of each track T, and this is thefunction of the circuit of FIG. 3. In this FIG. 3, like referencenumerals are used to indicate like elements shown in FIGS. 1 and 2. Therecording head 30, which will now be in the write mode, receives signalsfrom the oscillator 20 through the write trigger 24 and write driver 26to record information on the recording surface 12 of disk 10. Oscillator20 is activated by the output signals on a line 58 from an Or gate 60whose two inputs are the output on a line 62 from the memory 56 or theoutput of a sector format control 64 over a line 66. The sector formatcontrol 64 is well known in the art and functions to output digitalinformation which is to be recorded on the sector identification areas14, this information being, for example, synchronization bytes and othersector format information well known in the art. Format control 64 alsostarts memory 56 via a control signal on a line 68 to access the memory56 and record its addresses on the address recording area 14' of thesector identification areas 14. The head 36 and sector detector 34 areconnected over line 70 to format control 64 to activate control 64 atthe beginning of each sector S.

In the operation of the circuit of FIG. 3, when head 36 and sectordetector 34 detect a sector mark indicating the beginning of a sector Sof a given track T, the sector format control 64 will be activated tosequentially output digital sector format information through gate 60 tooscillator 20. Consequently, oscillator 20 will output signals inaccordance with this information from line 58 to enable recording head30 to write the required information on the area 14. When all of thissector format information is recorded, control 64 will output a signalon line 68 to access memory 56 at the memory location storing theaddress of a defective area within a particular sector S for a giventrack T. This address will be supplied through gate 60 to activateoscillator 20 which will then cause head 30 to write this address on theappropriate address recording area 14' of sector identification area 14.This operation continues with the recording head 30 over a single trackT until all the sectors S are written with the sector format anddefective area address information. Then, recording head 30 can be movedto a new track T and the circuit of FIG. 3 operated in a similar mannerto record the appropriate information on the areas 14 for each sector S.Of course, if a data recording area 16 of a given sector S of a giventrack T has no defective area, then no defective address will berecorded on the corresponding area 14.

The method of storing addresses of defective areas on disk 10 has beendescribed as first writing a test pattern on all the tracks, thenstoring addresses in memory 56 for all the tracks, and finally recordingthese addresses on all the tracks. However, this storing of addresses ofdisk 10 can be accomplished, for example, on a sector-by-sector basisfor each track. That is, first a given sector S of a given track T canhave a test pattern written on it with the circuit of FIG. 1. Then, thedisk 10 can be rotated to bring this given sector S under head 30 togenerate an address with the circuit of FIG. 2. Then, the disk 10 againcan be rotated to bring this given sector S under head 30 to record theaddress with the circuit of FIG. 3. After these three steps, a newsector S of the given track can be provided with an address to adefective area, and so on until all the sectors are accounted for. Then,the head 30 can be moved to a new track T to record such address on itssectors S in a similar manner.

After testing for defective areas on the recording surface 12 andidentifying any such areas by an address with the circuits of FIGS. 1-3,the disk 10 may now be distributed by the disk manufacturer for use witha disk drive having the circuits shown in FIGS. 5 and 6. The testing,however, as already noted, cound have been done on a customer disk driverather than at a disk factory. As will be described, this will enablethe user of the disk 10 and the disk drive shown in FIGS. 5 and 6 torecord and retrieve data on the recording surface 12, except on thedefective areas or potentially defective areas identified by theaddresses stored on the address recording areas 14' of the sectoridentification areas 14. Furthermore, it will be shown that the user canwrite or read data on the recording surface 12 without even being awarethat some areas of the data recording areas 16 may be defective. Thus,the user need not have to preplan the amount of data which can be storedon the disk 10 to account for any loss in capacity due to defectiveareas on the disk 10.

FIG. 5 illustrates a circuit 72 for writing digital data on the surface12 of disk 10. In this FIG. 5 like numerals again are used to indicatelike elements in the other figures. A disk drive control unit 74, wellknown in the art, has a number of inputs and outputs to control thewriting of data on the recording surface 12. The unit 74 has one input76 connected to the output of sector detector 34 and another input on aline 78 from the output of a sector counter 80 which counts the sectorsS from S₁ -S₁₆. Data to be recorded on recording surface 12 is suppliedby a central processing unit 80 as another input to the disk drivecontrol unit 74, this data being routed to oscillator 20 via an outputline 82 of the control unit 74. Another output line 84 couples thecontrol unit 74 to the read amplifier 42 to activate this amplifier toread the information recorded on the sector identification area 14 ofeach sector S, this amplified information being processed by aconventional amplitude detector 86 for delivery over a line 88 asanother input to the control unit 74. Addresses of the defective areason line 88 will be routed by the control unit 74 over an output line 90as one input to a comparator 92.

When head 36 and sector detector 34 detect a sector S, the signal online 76 instructs the disk drive control unit 74 to activate the readamplifier 42 via a signal on line 84 to couple and amplify theinformation read by head 30 via detector 86 into the control unit 74.This unit 74 will then output the defective area address onto line 90 asone input to the comparator 92. When the sector counter 80 reaches acount corresponding to the sector S on which data is to be recorded, thecontrol unit 74 will be activated to receive continuously the data fromCPU 80 and route it over line 82 to the oscillator 20 for recording onthe data recording area 16 of the particular sector S, and to activatecomparator 92 via a signal on a line 93.

Comparator 92 receives as another input on a line 94 the count in bytecounter 48 which receives the output of oscillator 20 via a line 96. Aseach bit of data is received by oscillator 20 over line 82, acorresponding output signal will be fed over line 96 and every eightbits or byte, counter 48 will have its count incremented by 1. Thecomparator 92 compares the address on line 90 to the count in counter 48and provides an output control signal over a line 98 having one of twolevels depending on whether a comparison is made.

The output signal from oscillator 20, which corresponds to the data overline 82, is fed over a line 100 as one input to an And gate 102 and asan input to a data delay or buffer 104 which is two bytes in length forreasons which will be described. The other input to the And gate 102 isthe output signal from comparator 92 on line 98. The output of buffer104 is fed over a line 106 as one input to another And gate 108. Theoutput signal on line 98 is also fed over a line 110 to an inverter 112whose output is then fed over a line 114 to a delay 116. The delay 116provides a two-byte delay of its input signal, which corresponds to thedelay of the data through the two-byte buffer 104, and provides anoutput signal on a line 118 as the other input to And gate 108. Anexclusive-Or gate 120 receives the output of And gate 102 or And gate108 to supply the data to the write trigger 24 and write driver 26 forrecording by the head 30.

As will be described further, the data signal from oscillator 20 on line100 will be processed to the recording head 30 via gates 102, 120, writetrigger 24 and write driver 26 without delay, or via buffer 104, gate108, gate 120, trigger 24 and driver 26 with buffer 104 providing adelay. In either event, the data will be received continuously from theCPU 80 when requested, though head 30 will not continuously record thisdate since the defective areas on disk 10 should be skipped. Also, itmay be noted that CPU 80 may be generally considered to be any data bankor supply, with the other circuit elements of FIG. 5 constituting a diskdrive for transferring data between this data supply and the disk 10.

In describing now the operation of the circuit 72 shown in FIg. 5,reference also will be made to the timing diagram of FIGS. 7A-7C. Assumethat data is to be stored on sector S₁ of track T₆₀₀ having a defectivearea identified with an address on the address recording area 14' of thesector identification area 14. The head 30 will be positioned over thistrack T₆₀₀ in accordance with well known disk drive servo circuitry. Themotor 38 also will be activated to rotate the disk 10 with the head 30over T₆₀₀.

When the beginning of sector mark on the sector identification area 14of sector S₁ is sensed by head 36 and detector 34, and output signal online 76 instructs the drive control unit 74 to activate the readamplifier 42 to amplify the information read by head 30 including thedefective area address recorded on the area 14'. This address will thenbe detected by detector 86 and fed through the control unit 74 as oneinput to the comparator 92. Also, sector counter 80 will have a count of1 corresponding to sector S₁, whereby control unit 74 will activatecomparator 92 via line 93 to perform its compare function. Then, at thebeginning of the data recording area 16 of sector S₁, the control unit74 will request and continously receive data from CPU 80, which will besupplied to the oscillator 20 whose output signal on line 100 willcorrespond to each bit of data at its input on line 82.

FIG. 7A shows the time that head 30 is over the data recording area 16of sector S₁. As the data recording area 16 of sector S₁ rotates beneathhead 30, the bits from oscillator 20 will be received by counter 48. Ifit is assumed in the present example that the defective area within thedata recording area 16 of sector S₁ is at bit 221, the address on line90 will correspond to byte 27. Until byte 27 is counted by counter 48,the comparator 92 will produce a high signal shown in FIG. 7b, whichwill enable gate 102 to deliver the bits through this gate andexclusive-Or gate 120 for writing by the head 30. Gate 108 also will beenabled for the first two bytes received since the output of two bytedelay 116 will not follow the output of inverter 112 low for a two-byteperiod; however, since buffer 104 is two bytes in length there will beno data to output from this buffer for a two byte period. At the end ofthis two byte period, gate 108 will be disabled.

Then, as the disk 10 continues to rotate, and the data is continuouslysupplied over line 82, counter 48 eventually will reach a count of 27corresponding to the address on line 90. Accordingly, the output ofcomparator 92 on line 98 will go low, as indicated in FIG. 7B;therefore, gate 102 will be disabled. Also, the output of inverter 112will go high, but the output of delay 116 will remain low for a two-byteperiod. Consequently, during this two byte period no data will besupplied to head 30 and this is the desired result since at this timethe head 30 will be over the defective area which, as mentionedpreviously, is assumed to be two bytes in length.

More specifically, when the comparator 92 goes low at the detection ofthe assumed defective area, bit 215 will be at the input stage of buffer104 and bit 200 will be at the output stage of buffer 104, with bits200-215 already being recorded via gate 102. Then, as disk 10 continuesto rotate and at the end of the two byte period, bits 216 through 231will be stored in buffer 104 with bit 216 being at the output stage andbit 231 being at the input stage of buffer 104. At this time, the outputof delay 116 will go high, as indicated in FIG. 7C; consequently, atthis time gate 108 will be enabled and remain enabled for the remainingdata recording area 16 beyond the assumed defective area to record bits216 to 4096 via buffer 104. At the end of the sector S₁, the circuit 72will be reset with reset signal (not shown), including the end of sectormark, to begin recording the data for another sector S of a track T in asimilar manner as sector S.sub. 1 of track T₆₀₀.

The circuit 72 has been described as not recording data on the defectivearea. However, such circuit may be modified to set the write trigger 24with the control unit 74, which may respond to the output of thecomparator 92 once the defective area is detected, to record constantfrequency, long wave data on such defective area. This long wave datawould then be used in a standard manner for resynchronizing a VCO(voltage controlled oscillator) (not shown) used for read-back of therecorded data. Without such long wave data, a change in phase of the VCOmight occur which could cause incorrect read-back. Other conventionalresynchronization techniques may also be used.

The fact that the present invention has the advantage of not reducingthe storage capacity of the recording surface 12 can be described in thefollowing way. Assume, as has already been indicated, that the bitcapacity of each sector S₁ -S₁₆ of a given track T is 4096 bits when thesectors are free of any defective areas. With such a defective area freedisk, all the space on a data recording area 16 of a given sector S canbe utilized to record these 4096 bits. However, if there is a defectivearea, in accordance with the one example of the present invention givenabove, there will be two bytes or sixteen bits of overhead or less spaceavailable on which to record the 4096 bits. Once this reduction inusable area 16 is known, then the motor 38 and oscillator 20 can bedesigned so that the speed of rotation of the disk 10 and the writefrequency is greater, proportionally to the size of the defective area,over a normal speed and frequency if the disk 10 had no defects. Inother words, in the example given, 512 bytes of data will now have tofit into a data recording area length of 510 bytes due to the defectivearea, rather than of 512 bytes. Since there is a two-byte reduction ofrecording space, the motor should be designed to have a speed which ishigher by 2/512 or about 0.004%. Also, the oscillation frequency ofoscillator 20 would be higher by a similar percentage, so that the datais being written faster to account for the less space available due tothe defective area. There will thus be, in effect, an increase in datadensity. It will be appreciated that the user of the disk drive 72 anddisk 109 need not even known of this increase in motor speed 38 andoscillation frequency 20, nor of the defective area; to the user, thedisk 109 and drive 72 will be able to record a full capacity of 4096bits on each sector S₁ -S₁₆ of each track T₁ -T₈₀₀.

It also will be appreciated from the above discussion that buffer 104should be of a certain size to avoid recording on the defective areas ofdisk 10. Generally, this size must be large enough to encompass themaximum number of bytes which may eventually be affected by a defectivearea initially on a disk 10 as manufactured, plus a number of bytesequal to any variation in byte count caused by the effect of changes inthe speed of motor 38 and the write frequency of oscillator 20 shown inFIG. 5 which would cause the byte count in counter 48 shown in FIG. 5 tochange. In other words, in the example given throughout this disclosure,a sector S or a track T on disk 10 as initially manufactured may be only1 bit in length, but eventually may grow longer to 10 bits. Also, anychange in motor speed or write frequency, such as an increase in thisspeed or frequency, may result in a comparison by comparator 92 soonerthan if no such increase occurred, since counter 48 will reach a countcorresponding to the address on line 90 quicker. As one example, abuffer 104 of 2 bytes in size is considered sufficient to account forthese factors under present technology.

With the data now recorded on the disk 10, a circuit 122 shown in FIG. 6may be utilized to read the data from recording surface 12. Again, likenumerals are used to indicate similar elements shown in FIG. 5. The diskdrive control unit 74 receives as one input over a line 124, the outputof the sector detector 34 and an input over a line 126 from the outputof sector counter 80. One output from disk drive control unit 74 is fedover a line 128 to the read amplifier 42 for amplifying the informationread by head 30, this information being detected by detector 86 and sentvia a line 130 to the control unit 74 as another input. Another outputfrom the disk drive control unit 74 is the address to a defective areawhich is fed on a line 132 as one input to the comparator 92, while ayet other output from unit 74 is a signal on a line 133 which activatescomparator 92 in response to the control unit input on line 126 fromsector counter 80. The disk drive control unit 74 also receives the dataread by head 30 from an exclusive-OR gate 134 via line 136 andcontinuously supplies this data from line 136 to an output line 138 fortransfer to the CPU 80.

The data from detector 86 on line 130 is also fed to counter 48 which isset to count data on a recording area 16 by a control signal on a line139 from unit 74 and which supplies an output corresponding to the countover a line 140 as the other input to comparator 92. The data on line130 is also fed through the buffer 104 as one input to an And gate 142and directly as one input to another And gate 144. The other input togate 142 is the output of a two-byte delay 145 on a line 146, whoseinput is the control signal from the output of comparator 92 on a line148. The other input to gate 144 is the output on a line 150 of aninverter 152 whose input is the output of comparator 92 on a line 148.As will be appreciated from the discussion below, even though head 30will not continuously read data recorded on a sector S of a track T dueto a data gap in view of the defective area, this data will becontinuously supplied at the output of gate 134 to continuously transferthe data to CPU 80.

In discussing the operation of circuit 122, it will be assumed that thedata recorded on sector S₁ of track T₆₀₀ with the circuit of FIG. 5, asalready discussed, is now desired to be read. The head 30 will be movedto track T₆₀₀ and the disk 10 rotated to place this sector S₁ under head30. Head 36 and sector detector 34 will provide an output on line 124when the beginning of sector mark is detected for sector S₁. In responseto the signal on line 124, the disk drive control unit 74 will activatethe amplifier 42 to amplify the information read by the head 30 so thatthe address on area 14' of sector S₁ to the defective area istransferred from detector 86 thgough the control unit 74 to line 132 asone input to comparator 92. Thereafter, when head 30 begins reading thedata recorded on the data recording area 16, the disk drive control unit74, in response to the signal on line 124 from sector detector 34 willactivate counter 48 via line 139 to begin counting the data bits fromdetector 86, and activate comparator 92 via line 133 in response to thesignal on line 126 from sector counter 80.

From the time recording head 30 begins sensing data on area 16 until thetime head 30 is over the defecting area the output of comparator 92 willbe high. This high signal will be delayed by two bytes by delay 145, asindicated in FIGS. 8A and 8B which show the total time that head 30 isoven area 16 and the output of delay 145, respectively. Also, the outputof comparator 92 will be inverted by inverter 152 to disable gate 144.Thus, for the fist 2 bytes no data will flow from gate 134 since gate144 will be disabled and buffer 104 will be receiving these 2 bytes withgate 142 also being disabled.

After this delay of two bytes, at which time bit 1 will be at the outputstage of buffer 104 and bit 15 at the input stage, gate 142 will beenabled, thereby gating the data from buffer 104 through gate 134 tocontrol unit 74 and ultimately to the CPU 80. When the head 30 reachesthe assumed defective area, the count in counter 48 will compare withthe address on line 132 so that the output of comparator 92 will go low.At this time gate 144 will be enabled by the output of inverter 152shown in FIG. 8C, but there will be no data from detector 86 since nodata will have been recorded on the defective area, except possibly thelong wave data used for resynchronization purposes already described.Gate 142 will continue to be enabled by the delayed output of delay 145to gate the data in buffer 104 which will be the two bytes immediatelypreceding the beginning of the defective area, including bits 200-215.Then, after this two-byte delay, the buffer 104 will have no data inview of the defective area, and the output of detector 86 will be bit216 recorded in the bit position next succeeding the defective area.Since gate 142 will now be disabled and gate 144 will be enabled untilthe end of sector S₁, the remaining data after the defective area datawill be transferred through gates 144 and 134 to the disk drive controlunit 74 and ultimately to CPU 80. Thus, it will be appreciated thatwhile head 30 does not continuously read the data recorded on surface 12in view of the gap provided by the defective area, the output of gate134 will be a continuous stream of read-back data which is continuouslyfed through control unit 74 to CPU 80. Of course, the circuit 122 may bemodified in any conventional manner (not shown) to read the long wavedata mentioned above for the resynchronization purposes.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand details may be made therein without departing from the spirit andscope of the invention.

What is claimed is:
 1. A method of transferring data between a datasupply and a disk file including a disk having a track divided intosectors, each sector having an address recording area followed by a datarecording area, and one sector having a defective area, comprising thesteps of:(a) detecting the defective area on the data recording area toidentify the defective area; (b) writing an address of the defectivearea on the address recording area; (c) recording data on the datarecording area of the one sector including;(i) continuously receivingdata from the data supply for recording on the one sector, (ii)detecting the defective area, with the address written on the addressrecording area; (iii) writing a first part of the received data on thedata recording area until the defective area is detected, (iv) delayingwriting the remaining part of the received data when the defective areais detected to avoid writing on the defective area, and (v) subsequentlywriting the remaining part of the data on the data recording areasucceeding the defective area; and (d) continuously delivering the datawritten on the data recording area to the data supply, including:(i)detecting the defective area with the address written on the addressrecording area; (ii) reading the data written on the data recordingarea; (iii) transferring with delay to the data supply the first part ofthe data read from the one sector between the beginning of the datarecording area and the defective area until the defective area isdetected; and (iv) transferring without delay to the data supply theremaining data read from the one sector succeeding the defective area.2. A method of transferring data between a movable recording medium anda data supply, the recording medium having a track divided into sectors,each sector having an address recording area and a data recording area,and one sector having a defective area within the data recording areaand an address of the defective area on the address recording area,comprising the steps of:(a) continuously receiving data from the datasupply for recording on the one sector; and (b) recording all of thereceived data on the data recording area of the one sector, except onthe defective area, by detecting the defective area, writing a firstpart of the received data on the data recording area until the defectivearea is detected, delaying writing the remaining part of the receiveddata when the defective area is detected to avoid writing on thedefective area, and subsequently writing the remaining part of the dataon the data recording area succeeding the defective area.
 3. A methodaccording to claim 2 wherein the step of delaying comprises:(a) feedingall the received data through a buffer; and (b) gating the data in thebuffer through a first gate commencing with the start of the remainingpart of the data.
 4. A method according to claim 3 wherein the step ofdetecting comprises:(a) reading the address to the defective area; (b)counting the received data as it is recorded on the data area andgenerating a count signal; (c) comparing the address to the countsignal; (d) generating a first control signal to gate the first part ofthe received data through a second gate until a comparison is madebetween the address and the count signal; and (e) generating a secondcontrol signal after the comparison is made to gate the remaining partof the data in the buffer.
 5. A method of transferring data between amovable recording medium and a data supply, the recording medium havinga track divided into sectors, each sector having an address recordingarea and a data recording area, and one sector having a defective areawithin the data recording area and an address of the defective area onthe address recording area, comprising the steps of:(a) continuouslyreceiving data from the data supply for recording on the one sector; (b)recording all of the received data on the data recording area of the onesector, except on the defective area; (c) reading information on the onesector including reading the data recorded on the data recording areaand reading the address of the defective area on the address recordingarea; and (d) continuously delivering the read data to the data supply,be detecting the defective area, transferring with delay to the datasupply the data recorded on the one sector between the beginning of thedata recording area and the defective area until the defective area isdetected, and transferring without delay to the data supply theremaining data recorded on the one sector succeeding the defective area.6. A method according to claim 5 wherein the step of transferring withdelay comprises:(a) feeding all the data read from the data recordingarea through a buffer; and (b) gating the data in the buffer through afirst gate until the defective area is detected.
 7. A method accordingto claim 6 wherein the step of transferring without delay comprisesgating the remaining data through a second gate after detection of thedefective area.
 8. Apparatus for transferring data between a data supplyunit and a storage medium having a track divided into a plurality ofsectors with each sector having an address recording area and a datarecording area, and at least one sector having an address on the addressrecording area of a defective area within the corresponding datarecording area, comprising:(a) means for continuously receiving datafrom the data supply to be stored on the one sector; and (b) means forrecording all of the received data on the data recording area of the onesector, except on the defective area, said means for recordingcomprising means for detecting the defective area, and means, connectedto said detecting means, for writing without delay a first part of thereceived data on the data recording area until the defective area isdetected and for writing with delay the remaining received data when thedefective area is detected to avoid writing on the defective area. 9.Apparatus according to claim 8 wherein said means for writingcomprises:(a) a recording head; (b) a buffer means through which thereceived data is fed; and (c) switchable gating means to gate the dataeither directly from the data receiving means to the recording head, orfrom the buffer means to the recording head.
 10. Apparatus according toclaim 9 wherein said means for detecting comprises:(a) means for sensingthe address; (b) means for counting the received data; and (c) means forcomparing the count in said counting means to the sensed address tocontrol said gating means.
 11. Apparatus for transferring data between adata supply unit and a storage medium having a track divided into aplurality of sectors with each sector having an address recording areaand a data recording area, and at least one sector having an address onthe address recording area of a defective area within the correspondingdata recording area, comprising:(a) means for continuously receivingdata from the data supply to be stored on the one sector; (b) means forrecording all of the received data on the data recording area of the onesector, except on the defective area; (c) means for reading the datarecorded on the one sector; (d) means for continuously feeding the readdata to the data supply unit, said means for continuously feedingcomprising means for detecting the defective area, buffer means toreceive the read data, and switchable gating means to gate the read dataeither out of said buffer means to said means for continuously feedinguntil the defective area is detected or directly to said means forcontinuously feeding after defective area is detected.
 12. Apparatusaccording to claim 11 wherein said means for detecting comprises:(a)means for sensing the address; (b) means for counting the read data; and(c) means for comparing the count in said counting means to the sensedaddress to control said gating means.